ASK TOM WHY.

Dear Tom, In an answer to a question about global...

In an answer to a question about global warming, you said a warmer climate would be a wetter one. Why would that happen?

Ronald Lavet

Dear Ronald,

It's true. Higher planetary temperatures mean heavier precipitation because more water vapor can be contained in air at higher temperatures than at lower temperatures. In general, a storm system will produce more precipitation when it draws moist air into its circulation than when it has less moisture to work with.

But a note of caution: Precipitation increases driven by higher global temperatures are not likely to be uniform across the Earth. Computer simulations of global weather patterns tell us that changed climates induced by higher temperatures will yield greater precipitation overall, but may actually bring drier conditions in some areas of the world.

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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.